The invention relates to selective plastic expansion of tubings. More particularly the invention relates to selectively expanding a steel tubing to create recesses in the tubing by application of a radial force to the interior of the tubing.
Numerous methods and devices are known for expansion of tubings.
PCT patent application WO 93/25799, published Dec. 23, 1993, discloses a method of expanding a casing against the wall of an underground borehole wherein the casing is made of a malleable material which preferably is capable of plastic deformation of at least 10% unaxial strain and the casing may be expanded by an expansion mandrel which is pumped, pulled or pushed through the casing.
Other expansion methods and devices are disclosed in German patent specification No. 1583992 and in U.S. Pat. Nos. 3,203,483; 3,162,245; 3,167,122; 3,326,293; 3,785,193; 3,499,220; 5,014,779; 5,031,699; 5,083,608 and 5,366,012.
Many of the known expansion methods employ an initially corrugated tube and the latter prior art reference employs a slotted tube which is expanded downhole by an expansion mandrel.
The use of corrugated or slotted pipes in the known methods serves to reduce the expansion forces that need to be exerted to the tube to create the desired expansion.
It is an object of the present invention to provide a method for selective expanding an at least partly solid, i.e. unslotted, tubing which requires exertion of a force to expand the tubing and which provides a tubing having at one or more sections a larger diameter and possibly higher strength than the unexpanded tubing and which can be carried out with a tubing which already may have a tubular shape before expansion.
The present invention therefore relates to a method of selective plastic expansion of sections of a tubing to create one or more recesses (cavity bulges) in the tubing with a larger diameter than that of the original tubing in which the tubing is radially symmetrically or asymmetrically expanded at one or more locations by application of a radial force to the interior of the tubing thereby inducing a plastic radial deformation of the tubing and removing said radial force from the interior of the tubing.